Disease relevance of SLC9A3

• Expression levels of the cystic fibrosis transmembrane regulator (CFTR) (Cl- channel), SLC26A3 (Cl-/HCO exchanger) and SLC9A3 (Na+/H+ exchanger) mRNAs were measured by real-time quantitative RT-PCR in peroperative colonic samples from controls (n = 4) and patients with ulcerative colitis (n = 10) [1].
• OBJECTIVES: The objectives of this study were to identify polymorphic variants within the gene coding for the sodium/hydrogen exchanger type 3 (NHE3) and to examine their relationship with hypertension and biochemical indices of sodium balance [2].
• These albumin-induced increases in expression and activity of NHE3 in PTC suggest a possible mechanism for Na+ retention in response to proteinuria [3].
• Chronic metabolic acidosis markedly increases HCO3- absorptive capacity of MTAL, by stimulating at least the synthesis of apical NHE-3 protein, as in the proximal tubule [4].
• The paradoxical increase in HCO3- absorptive capacity of MTAL observed in the model of chronic NaHCO3-load alkalosis should be due to other factors overcoming the inhibitory effect of alkalosis on NHE-3 [4].

Psychiatry related information on SLC9A3

• OBJECTIVES: To further explore the possible role of this exchanger for the control of breathing, we examined the individual relationship between brainstem NHE3 abundance and ventilation in rabbits during wakefulness [5].
• The protein abundance of mTAL BSC1, NHE3, and Na+ pump increased significantly in young but remained unchanged in 7-month-old rats subjected to water deprivation [6].

High impact information on SLC9A3

• Moreover, TNF, but not LIGHT, inhibited Na(+) absorption due to TNF-induced internalization of the brush border Na(+)/H(+) exchanger NHE3 [7].
• Using isoform-specific primers, mRNA transcripts of the Na(+)/H(+) exchangers NHE1, NHE2, and NHE3 were detected by RT-PCR, and identities were confirmed by sequencing [8].
• Functional NHE1 and NHE3 activities were identified at the basolateral and apical membranes, respectively [8].
• 10(-7) M and 10(-8) M hydrocortisone increased NHE3 activity, and in their presence, acid incubation further increased NHE3 activity [9].
• In addition, hypertonicity increased total cellular and plasma membrane NHE3 protein abundance twofold, with only a small increase in NHE3 mRNA abundance [10].

Chemical compound and disease context of SLC9A3

• Conclusion: These results suggest that exposure of PTCs to high glucose concentrations promotes osmolality mediated cell hypertrophy and increased tubular albumin reabsorption linked to an increase in NHE-3 expression [11].
• Acute CPA-induced control of NHE3 was blocked by antagonists of A1 adenosine receptors and inhibition of phospholipase C, pretreatment with BAPTA-AM (chelator of cellular calcium), and exposure to pertussis toxin [12].
• The nonreceptor tyrosine kinase, c-Src, plays a key role in regulation of NHE3 by acidosis in the proximal tubule, and in signaling effects of angiotensin II in vascular smooth muscle [13].
• NHE3 is acutely up- and downregulated in response to some G protein-linked receptors, tyrosine kinase receptors, and protein kinases when studied in intact ileum, when stably expressed in PS120 fibroblasts, and in the few studies reported in the human colon cancer cell line Caco-2 [14].
• Levels of urinary NHE3 normalized to urinary creatinine level were increased in patients with prerenal azotemia and 6 times as much in patients with ATN, without overlap (ATN, 0.78 +/- 0.36; prerenal azotemia, 0.12 +/- 0.08; P < 0.001) [15].

Biological context of SLC9A3

• The data show that initiation of Na(+)-glucose cotransport resulted in rapid increases in both apical membrane-associated NHE3 and cytoskeletal-associated ezrin and occurred in parallel with ezrin phosphorylation at threonine 567 [16].
• 2) Decreased surface expression due to decreased rates of exocytosis and plasma membrane delivery of newly synthesized NHE3, with normal total expression levels and slightly reduced endocytosis rates [17].
• Cyclic AMP is a major second messenger that inhibits the brush border Na+/H+ exchanger NHE3 [18].
• Point mutations of these positively charged aa reduced (NHE3 double mutant [R520F, R527F]) or abolished (NHE3 triple mutant [K516Q, R520F, R 527F]) ezrin binding [17].
• RME, but not fluid-phase endocytosis, was dependent on NHE3 activity and expression [19].

Anatomical context of SLC9A3

• Initiation of Na(+)-glucose cotransport in intestinal epithelial cells leads to activation of the apical Na(+)-H(+) exchanger NHE3 and subsequent increases in cytoplasmic pH (pH(i)) [16].
• Initiation of Na(+)-glucose cotransport in intestinal absorptive epithelia causes NHE3 to be translocated to the apical plasma membrane, leading to cytoplasmic alkalinization [20].
• Based on physiological studies, the epithelial brush-border (BB) Na+/H+ antiporter3 (NHE3) seems to associate with the actin cytoskeleton both by binding to and independently of the PDZ domain containing proteins NHERF1 and NHERF2 [17].
• Immunocytochemistry localises NHERF1 (NHE3 regulatory factor 1) to the apical portion of Caco-2 cells where it will interact with NHE3 and allow PKA-mediated phosphorylation of NHE3 [21].
• Experiments using brush border membranes and cultured renal proximal tubule cells indicate a specific requirement for NHERF-1 for cAMP-mediated phosphorylation and inhibition of NHE3 [22].

Associations of SLC9A3 with chemical compounds

• At least two luminal transporters mediate HCO(3)(-) salvage, the Na(+)/H(+) exchanger (NHE3) and the Na(+)-HCO(3)(-) cotransport (NBC3) [23].
• Forskolin and VIP inhibit pH(i) recovery (NHE3 function) from beta-alanine-induced intracellular acidification [21].
• Using confocal microscopy with a novel antibody raised against the predicted extracellular NH2 terminus of human NHE3, we observed in nonpermeabilized cells that exposure of PTC to albumin (0.1 and 1.0 mg/ml) increased NHE3 at the cell surface to 115.4 +/- 2.7% (P < 0.0005) and 122.4 +/- 3.7% (P < 0.0001) of control levels, respectively [3].
• Moreover, there was an additional, equivalent increase (P < 0.05) in duodenal HCO(3)(-) output with 10(-3) M amiloride, which inhibited NHE3 [24].
• SCFA increase intestinal Na absorption by induction of NHE3 in rat colon and human intestinal C2/bbe cells [25].

Physical interactions of SLC9A3

• E3KARP binds an internal region within the NHE3 C-terminal cytoplasmic tail, defining a new mode of PDZ domain interaction [18].
• In a previous work, we show that CFTR interacts with NHE3 to regulate its activity (Ahn, W., Kim, K. W., Lee, J. A., Kim, J. Y., Choi, J. Y., Moe, O. M., Milgram, S. L., Muallem, S., and Lee, M. G. (2001) J. Biol. Chem. 276, 17236-17243) [23].
• We now show that NHE3 directly binds ezrin at a site in its C terminus between aa 475-589, which is separate from the PSD95/dlg/zonular occludens-1 (PDZ) interacting domain [17].
• The intestinal and renal proximal tubule brush border (BB) Na+-H+ exchanger NHE3 binds to members of the NHERF (Na+-H+ exchanger regulatory factor) family [26].
• Taken together, these findings indicate that a significant pool of NHE3 exists as a multimeric complex with megalin in the brush border of the proximal tubule [27].

Co-localisations of SLC9A3

• Instead, NHE3 colocalized with transferrin receptors and with cellubrevin, markers of recycling endosomes [28].

Regulatory relationships of SLC9A3

• NHERF-1/EBP50 was previously shown to regulate Na(+)/H(+)-exchanger 3 (NHE3) activities in OK cells [29].
• Akt2 phosphorylates ezrin to trigger NHE3 translocation and activation [20].
• In conclusion, we have shown that amino acid uptake via hPAT1 is inhibited by activators of the cAMP pathway indirectly through inhibition of NHE3 activity [21].
• In addition, proximal duodenal mucosal HCO(3)(-) transport was measured in humans in vivo in response to luminal perfusion of graded doses of amiloride; 10(-5)--10(-4) M amiloride was used to inhibit NHE2 and 10(-3) M amiloride to inhibit NHE3 [24].
• Our data indicate that IFN-gamma and TNF-alpha may repress the NHE3 promoter activity in C2BBe1 cells by PKA-mediated phosphorylation of Sp1 and Sp3 transcription factors [30].

Other interactions of SLC9A3

• In intact epithelia, PAT1-mediated amino acid influx is reduced under conditions in which NHE3 is inactive [31].
• The distributions of NHE3 and E3KARP were not affected by treatment with 8-bromo-cAMP [18].
• We reported recently that this NHE3 translocation requires ezrin phosphorylation [20].
• Pharmacological Akt inhibition or Akt2 knockdown also prevented NHE3 translocation and activation after initiation of Na(+)-glucose cotransport, confirming the functional role of Akt2 [20].
• The complementary DNA (cDNA) sequences of NHE1 to NHE3 and NHE5 are known in humans [32].

Analytical, diagnostic and therapeutic context of SLC9A3

• Molecular cloning and functional analysis of the human Na(+)/H(+) exchanger NHE3 promoter [33].
• After treatment with cytokines, the binding of Sp1 and Sp3 proteins to NHE3 promoter decreased significantly, as seen by gel mobility shift assays and chromatin immunoprecipitation assays [30].
• In situ hybridization technique was used to localize NHE-2 and NHE-3 mRNA in the colon [34].
• NHE-3 knockouts are hypotonic and can not survive on low salt diet [35].
• METHODS: The localization of Akt, PI 3-K, and NHE3 was determined by either immunocytochemistry and/or membrane fractionation using OptiPrep density gradient centrifugation [36].

References